You don't need to copy the Nandroid to PC, no.
Factory reset/wipe data
Wipe Dalvik Cache
Flash new ROM
(Optionally flash theme)
(Optionally flash overclocked/undervolted kernal)
Pretty much wipe anything you can... hell, give the screen a wipe while you wait!
.
Oh and I agree, VillainRom is definately worth looking at SiHH, I've had no crashes or anything and I have no problem with battery life using it with Ninphetamine.
If I got one of these on three, will it be stacked out with three's bloatware?
I like the look of three's all you can eat data package compared to t-mobile unlimited but with fair use. Nice cash back deals on at the moment as well.